164 TELEOSTEI : HETEROSOMATA. — XXI. 
young are symmetrical, one eye on each side, the body is translu- 
cent and the fish is vertical in the water. The processes by which 
the eye of the lower side becomes transferred through or over the 
head to the other side are very curious and interesting. There is 
but one family. (€repds different ; cépa, body.) 
Famity LXXXIX. PLEURONECTIDA. (Tus 
FLOUNDERS.) 
Body strongly compressed, the cranium twisted so that both eyes 
are on the colored side; mouth and dentition various; premaxil- 
laries protractile ; maxillary simple; pseudobranchie present. Gills 
4; no air bladder; vent not far behind head ; scales various; fins 
without spines. D. very long; A. similar, shorter; P. and V. vari- 
ous. Fishes mostly carnivorous, chiefly found on sandy sea-bottoms, 
some of them ascending rivers. Genera 50; species 450. Those 
species found in Arctic seas have, as usual, an increased number of 
vertebrz ; the tropical forms have 30 to 35; the others 40 to 70. 
a, Flounders: Edge of preopercle free; teeth present; P. and V. well developed 
(with rare exceptions). 
6. Mouth nearly symmetrical, the teeth nearly ae on the two sides, the 
gape usually but not always wide. 
c. Ventral fins symmetrical, similar in position and i in form of base, the 
ventral of eyed side not extended along the ridge of abdomen. 
(Hippoglossine.) 
d. Vertebre and fin rays much increased in number (vertebre about 
50; D.100; A.85); body elongate; C. lunate; lateral line simple; 
no anal spine; eye on right side. 
e. Lateral line without arch. . . . PLATYSOMATICHTHYS, 226. 
ee. Lateral line with an arch anteriorly. . . H1proGiossus, 227. 
dd. Vertebrex and fin rays in moderate number; (Vert. less than 46; 
D. less than 95; A. less than 75); C. double truncate. 
J. Lateral line without arch; vertebra 45; = on on right side; scales 
firm, ciliated; spine ‘before A. strong; D. beginning above eye. 
HirroGossoipgs, 228. 
Jf. Lateral line arched in front; vertebre 35 to 41; eyes on left side; 
scales nearly smooth; anal spine weak; D. beginning before 
eye: «& « ee * + « « « + PARALICHTHYS, 229. 
cc. Ventral fins unsymmetrical, “dissimailar i in position or in form; the left 
V. extended along ridge of abdomen; eyes on left side. (Pleu- 
ronecting.) 
g- Vomer with teeth; lateral line arched in front; vertebra 31 to 
86; mouth large; teeth in bands; form broad-ovate; scales 
cycloid, small or wanting; interorbital space not concave. 
PLEURONECTES, 230. 
gg- Vomer toothless; V. free from As Vert. 34 to 40. 
i. Lateral line arched in front; teeth small, in 1 or 2 series; in- 
terorbital space broad, concave; scales small, ctenoid. 
PLaTorarys, 231. 
